Conventionally, hybrid vehicles that are switchable between running using a motor for driving (so called EV running) and running using the motor and an engine for driving (so called HEV running) are known. In the above-described hybrid vehicle, a technique for previously planning a switching between the EV running and the HEV running based on a route information and gradient information of a navigation system is known.
The switching control of the EV running and the HEV running is disclosed, for example, in the following patent document 1. The patent document discloses a hybrid vehicle that is switchable between the EV running and the HEV running. The hybrid vehicle includes an external battery charger that charges a battery with an external power source, a map information device that can identify a present location of a vehicle on map data, base registration means that registers a location where the external power source is installed as a base on the map data of the map information device, EV running area registration means that registers area where the EV running is possible centering around the base on the map data of the map information device, outward trip EV running means that executes the EV running in the EV running possible area when the hybrid vehicle starts from the base in a state that the external battery charger charges the battery with the external power source.
In the hybrid vehicle, a center value of battery charge amount (SOC) is fixed. Thus, when the hybrid vehicle goes downhill and a battery charging progresses, as shown in FIG. 5A, the battery charge amount reaches a charge limit (SOXmax: a state where electricity cannot be recovered (charged) any more) during going downhill. As a result, a recovery loss of a regenerative charging occurs.
Thus, as shown in FIG. 5B, a study of a technique for recovering regenerative energy without loss during going downhill by previously switching to the EV running on a flat load before downhill running and reducing the battery charge amount has been conducted.
As a result, as shown in FIG. 6, in a case where the battery charge amount is not reduced before going downhill (a conventional art 1 in FIG. 6), a recovery loss Sm of regenerative charging occurs. However, in a case where the battery charge amount is reduced before is (sec) of the downhill running in prospect of the recovery loss Sm of the regenerative charging (a conventional art 2 in FIG. 6), the regenerative charging is performed throughout the downhill running.
In a case where there is an uphill in front of a downhill as shown in FIG. 7, if the EV running is performed on the uphill for reducing the battery charge amount, a feeling of strangeness in running may be caused. Thus, in this case, it is preferable to consume a sufficient battery charge amount at least until the hybrid vehicle reaches the uphill (that is, a distance L short of the uphill).
However, the present inventors found that even when the hybrid vehicle switches to the EV running before the downhill, a recovery loss of the regenerative charging may occur. Namely, in a battery, such as a nickel hydride battery, used for a hybrid vehicle, a limit temperature is set for securing reliability. A temperature of the battery is monitored with a temperature sensor, and when the battery exceeds the limit temperature, safety function works and charge and discharge is stopped forcibly. As a result, charging is not performed even during the downhill running that is a running condition in which a regenerative charging is possible, and a recovery loss of the regenerative charging occurs.